The present invention relates to a data processing apparatus consisting of a memory unit and a data processor processing data according to a program stored in the memory unit.
Heretofore there are known microprocessors based on the real-time operating system nucleus (hereinbelow called TRON) specification.
Since the microprocessor based on this TRON specification is a data processor formed on a semiconductor chip, it is called a TRON specification chip.
In the instruction set specification of this TRON specification chip the orthogonality (independency) of the instruction function and the addressing mode is taken into account and a memory-memory operation is possible in a general type instruction. Consequently there are two addressing fields in one instruction.
Further this general type instruction has an instruction basic portion composed of 4 bytes and an addressing extension portion of 0 to 4 bytes. The instruction basic portion is divided into a first half word and a second half word composed of 2 bytes, respectively. The first half word designates a first operand and the second half word designates a second operand and an instruction operation.
The address extension portion (0 to 4 bytes) in the first operand succeeds the first half word of the instruction basic portion and the address extension portion (0 to 4 bytes) in the second operand succeeds the second half word of the instruction basic portion.
Further the addressing field in the first half word and the addressing field in the second half word are at an identical bit position. Consequently it is possible to carry out the processing of the addressing mode and the operation of an instruction, considering the first half word and the second half word as different instructions (intermediate instructions).
The unit of this processing is called step code and an example, in which the general type instruction based on the TRON specification is carried out by dividing it into two steps, is described in Report of Technical Researches of the Electronic Information Communication Society, CPSY 87-53 (March 1987), pp. 25-30 (in Japanese).